Electro-hydrodynamic (“EHD”) energy conversion is a process wherein electrical energy is extracted from the kinetic energy of a flowing fluid, such as a wind stream. As illustrated in FIG. 1, and described in detail in U.S. application Ser. No. 12/357,862 and PCT application PCT/US09/31682, an EHD wind system emits a fine mist of charged particles of a single polarity into a wind stream, wherein the wind stream separates the charges from the oppositely charged source. As wind drag moves charged particles from a charge source (isolated from electrical ground) to a downstream collector (coupled to electrical ground), charge source becomes charged to an electric potential (system voltage/system potential). When the charged particles are positive, the system potential is negative with respect to ground, and vice versa. In prior art EHD systems, charging of the system is self-limiting. As the system charges to ever higher system voltages, the drag force of the wind must overcome a larger back force from the electric field (system field), generated by the system potential, that is directed from electrical ground to the charge source. Additionally, the distribution of charged particles between the charge source and the downstream collector, also known as a space charge, creates a second electric field that further hinders charged particle movement by the wind. When the drag force of the wind and the sum of the fields created by the system potential and the space charge are in equilibrium, the EHD system reaches a steady state. In steady state, the system no longer charges to a large system potential (in magnitude), which results in a drop in extracted power. Unfortunately, the system potential cannot simply be increased to extract more power—an increase system potential above a steady state condition typically results in a reduction in the current running from the charge source to ground. This is because some of the current will be deflected to a conductor of the EHD system as the large system field shorts the charged particles to the conductor. Thus, the extracted power will not increase.
This invention provides a new and useful system and method of controlling the field magnitude at the charging source.